No convincing evidence the hippocampus is associated with working memory
Scott D. Slotnick
Abstract
In a previous discussion paper , twenty-six working memory fMRI studies that reported activity in the hippocampus were systematically analyzed. None of these studies provided convincing evidence that the hippocampus was active during the late delay phase, the only period in which working memory can be isolated from long-term memory processes. Based on these results, it was concluded that working memory does not activate the hippocampus. Six commentaries on the discussion paper were received from Courtney (2022 Courtney, S. M. (2022). Working memory is a distributed dynamic process. Cognitive Neuroscience, 13(3–4), 208–209. July, Epub 2022 Oct 6. PMID: 36200905. https://doi.org/10.1080/17588928.2022.2131747[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), Kessels and Bergmann (2022 Kessels, R. P. C., & Bergmann, H. C. (2022). What does the hippocampus do during working-memory tasks? A cognitive-neuropsychological perspective. Cognitive Neuroscience, 13(3–4), 210–211. July, Epub 2022 Oct 11. PMID: 36218275. https://doi.org/10.1080/17588928.2022.2131745[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), Peters and Reithler (2022 Peters, J. C., & Reithler, J. (2022). Hippocampal activity in working memory tasks: Sparse, yet relevant. Cognitive Neuroscience, 13(3–4), 212–214. July, Epub 2022 Oct 9. PMID: 36209434. https://doi.org/10.1080/17588928.2022.2131746[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), Rose and Chao (2022 Rose, N. S., & Chao, C. M. (2022). Hippocampal involvement in working memory following refreshing. Cognitive Neuroscience, 13(3–4), 215–217. July, Epub 2022 Oct 11. PMID: 36218261. https://doi.org/10.1080/17588928.2022.2131749[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), Stern and Hasselmo (2022 Stern, C. E., & Hasselmo, M. E. (2022). Mechanisms for maintaining information in working memory. Cognitive Neuroscience, 13(3–4), 218–219. July, Epub 2022 Oct 10. PMID: 36214597; PMCID: PMC10121215. https://doi.org/10.1080/17588928.2022.2131750[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), and Wood et al. (2022 Wood, J. L., Clark, D. E., & Nee, D. E. (2022). Hippocampal activity supporting working memory is contingent upon specific task demands. Cognitive Neuroscience, 13(3–4), 220–222. July, Epub 2022 Oct 6. PMID: 36200870. https://doi.org/10.1080/17588928.2022.2131748[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]). Based on these commentaries, the present response paper considered whether there is evidence of sustained hippocampal activity during the working memory delay period based on depth-electrode recording, whether there are activity-silent working memory mechanisms in the hippocampus, and whether there is hippocampal lesion evidence indicating this region is important for working memory. There was no convincing electrophysiological or neuropsychological evidence that the hippocampus is associated with working memory maintenance, and activity-silent mechanisms were arguably speculative. Given that only a small fraction (approximately 5%) of working memory fMRI studies have reported hippocampal activity and lesion evidence indicates the hippocampus is not necessary for working memory, the burden of proof is on proponents of the view that the hippocampus is important for working memory to provide compelling evidence to support their position. To date, from my perspective, there is no convincing evidence that the hippocampus is associated with working memory.